ATP-binding cassette transporter controls leaf surface secretion of anticancer drug components in Catharanthus roseus

Integration of a Decrescent Transcriptome and Metabolomics Dataset of Peucedanum praeruptorum to Investigate the CYP450 and MDR Genes Involved in Coumarins Biosynthesis and Transport

Peucedanum praeruptorum Dunn is well-known traditional Chinese medicine. However, little is known in the biosynthesis and the transport mechanisms of its coumarin compounds at the molecular level. Although transcriptomic sequence is playing an increasingly significant role in gene discovery, it is not sufficient in predicting the specific function of target gene. Furthermore, there is also a huge database to be analyzed. In this study, RNA sequencing assisted transcriptome dataset and high-performance liquid chromatography (HPLC) coupled with electrospray-ionization quadrupole time-of-flight mass spectrometry (Q-TOF MS)-based metabolomics dataset of P. praeruptorum were firstly constructed for gene discovery and compound identification. Subsequently, methyl jasmonate (MeJA)-induced gene expression analysis and metabolomics analysis were conducted to narrow-down the dataset for selecting the candidate genes and the potential marker metabolites. Finally, the genes involved in coumarins biosynthesis and transport were predicted with parallel analysis of transcript and metabolic profiles. As a result, a total of 40,952 unigenes and 19 coumarin compounds were obtained. Based on the results of gene expression and metabolomics analysis, 7 cytochrome-P450 and 8 multidrug resistance transporter unigenes were selected as candidate genes and 8 marker compounds were selected as biomarkers, respectively. The parallel analysis of gene expression and metabolites accumulation indicated that the gene labeled as 23,746, 228, and 30,922 were related to the formation of the coumarin core compounds whereas 36,276 and 9533 participated in the prenylation, hydroxylation, cyclization or structural modification. Similarly, 1462, 20,815, and 15,318 participated in the transport of coumarin core compounds while 124,029 and 324,293 participated in the transport of the modified compounds. This finding suggested that integration of a decrescent transcriptome and metabolomics dataset could largely narrow down the number of gene to be investigated and significantly improve the efficiency of functional gene predication. In addition, the large amount of transcriptomic data produced from P. praeruptorum and the genes discovered in this study would provide useful information in investigating the biosynthesis and transport mechanism of coumarins.

Involvement of the leaf-specific multidrug and toxic compound extrusion (MATE) transporter Nt-JAT2 in vacuolar sequestration of nicotine in Nicotiana tabacum

Alkaloids play a key role in higher plant defense against pathogens and herbivores. Following its biosynthesis in root tissues, nicotine, the major alkaloid of Nicotiana species, is translocated via xylem transport toward the accumulation sites, leaf vacuoles. Our transcriptome analysis of methyl jasmonate-treated tobacco BY-2 cells identified several multidrug and toxic compound extrusion (MATE) transporter genes. In this study, we characterized a MATE gene, Nicotiana tabacum jasmonate-inducible alkaloid transporter 2 (Nt-JAT2), which encodes a protein that has 32% amino acid identity with Nt-JAT1. Nt-JAT2 mRNA is expressed at a very low steady state level in whole plants, but is rapidly upregulated by methyl jasmonate treatment in a leaf-specific manner. To characterize the function of Nt-JAT2, yeast cells were used as the host organism in a cellular transport assay. Nt-JAT2 was localized at the plasma membrane in yeast cells. When incubated in nicotine-containing medium, the nicotine content in Nt-JAT2-expressing cells was significantly lower than in control yeast. Nt-JAT2-expressing cells also showed lower content of other alkaloids like anabasine and anatabine, but not of flavonoids, suggesting that Nt-JAT2 transports various alkaloids including nicotine. Fluorescence assays in BY-2 cells showed that Nt-JAT2-GFP was localized to the tonoplast. These findings indicate that Nt-JAT2 is involved in nicotine sequestration in leaf vacuoles following the translocation of nicotine from root tissues.

A look inside an alkaloid multisite plant: the Catharanthus logistics

Environmental pressures forced plants to diversify specialized metabolisms to accumulate noxious molecules such as alkaloids constituting one of the largest classes of defense metabolites. Catharanthus roseus produces monoterpene indole alkaloids via a highly elaborated biosynthetic pathway whose characterization greatly progressed with the recent expansion of transcriptomic resources. The complex architecture of this pathway, sequentially distributed in at least four cell types and further compartmentalized into several organelles, involves partially identified inter-cellular and intra-cellular translocation events acting as potential key-regulators of metabolic fluxes. The description of this spatial organization and the inherent secretion and sequestration of metabolites not only provide new insight into alkaloid cell biology and its involvement in plant defense processes but also present new biotechnological challenges for synthetic biology.

Making iridoids/secoiridoids and monoterpenoid indole alkaloids: progress on pathway elucidation

Members of the Acanthaceae, Apocynaceae, Bignoniaceae, Caprifoliaceae, Gentianaceae, Labiatae, Lamiaceae, Loasaceae, Loganiaceae, Oleaceae, Plantaginaceae, Rubiaceae, Saxifragaceae, Scrophulariaceae, Valerianaceae, and Verbenaceae plant families are well known to accumulate thousands of bioactive iridoids/secoiridoids while the Apocynaceae, Loganiaceae and Rubiaceae families also accumulate thousands of bioactive monoterpenoid indole alkaloids (MIAs), mostly derived from the secologanin and tryptamine precursors. Several large-scale RNA-sequencing projects have greatly advanced the tools available for identifying candidate genes whose gene products are involved in the biosynthesis of iridoids/MIAs. This has led to the rapid comparative bioinformatics guided elucidation of several key remaining steps in secologanin biosynthesis as well as other steps in MIA biosynthesis. The availability of these tools will permit broad scale biochemical and molecular description of the reactions required for making thousands of iridoid/MIAs. This information will advance our understanding of the evolutionary and ecological roles played by these metabolites in Nature and the genes will be used for biotechnological production of useful iridoids/MIAs.